Port 6556Checkmk Monitoring Agent

Checkmk monitoring servers poll agents on TCP 6556 for host, service, and plugin data.

transport: tcp
in transit: encrypted
assignment: official
risk: 6/10
lookups: 0

also known as checkmk-agent, Checkmk agent port

Technical Details

what runs on :6556

The Checkmk agent listens for TCP connections, normally on port 6556, and supplies monitoring data in a line-oriented text format divided into sections such as <<<check_mk>>> and <<<df>>>; installed agent plugins can add further sections. Classic agents return the data directly and use an unencrypted connection. Modern deployments use the Checkmk agent controller, which supports TLS-protected communication after the agent is registered with the Checkmk site. The monitoring server initiates the connection; this is not a general-purpose interactive shell.

Security Information

exposure of :6556

risk score

6/ 10risk

treat as sensitive. widely scanned and regularly exploited when reachable — restrict it to known sources.

network services averages 2.6 across 1,725 ports — this one sits 3.4 above.

in transit

encrypted

payloads are protected on the wire

assignment

official

registered with iana for this service — scanners fingerprint it by number

reachable over

tcp

every listening transport is another surface to filter at the edge

security overview

Agent output can disclose host configuration, software, processes, filesystems, and data collected by plugins. Restrict access to the Checkmk server or trusted monitoring network; do not expose the port to the public internet. Registered modern agents can use TLS, but legacy or unregistered configurations may expose output in cleartext, and plugin output can contain sensitive information.

Record

iana registry entry

port: :6556
service: Checkmk Monitoring Agent
transport: TCP
encryption: tls / encrypted
assignment: iana registered
risk: 6/10risk
category: Network Services System
usage: A Checkmk site connects to this port on monitored hosts to collect system and application metrics. It is typically reachable only from the monitoring server; older or legacy agents may return their data without transport encryption.
lookups: 0rank 993
added: 2026-10-10
updated: 2026-10-10
references: IANA service name registry — port 6556

Something wrong?

This record is maintained by the engineers who use port 6556. Every field on it is editable — change what's wrong, say how you know, and a reviewer publishes it, usually within a minute. Last touched 2026-10-10.

01edit any field on a page of its own
02a model checks it for accuracy and spam
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edit this record →back to the registry

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risk mix of the 8 listed

caution100%

0 of 8 encrypted

Port :6556Checkmk Monitoring Agent

Technical Details

Security Information

Related Ports

Port 6556Checkmk Monitoring Agent